Satellite unfurlable antenna array

ABSTRACT

Disc on rod antenna radiating elements having bifilar helix feeds are arranged in a particular concentric circle type array configuration to achieve high gain, improved elipticity and size and weight economies. Element spacing is adjusted to prevent element collecting aperture overlap. A collapsible segmented dielectric rod in combination with ring members of radial wire segments are utilized to provide an unfurlable array in one preferred embodiment.

, D United States Patent [151 3,702,481

Koller et al. [4 1 Nov. 7, 1972 [54] SATELLITE UNFURLABLE ANTENNA [56] References Cited ARRAY [72] I w B K e Ak R be" B UNITED STATES PATENTS t lam o r ron; o Higgins, uniomgwn; James 3,257,660 6/1966 Schneider ..343/7ss Hayk, Akron 3 of Ohio 3,202,998 8/1965 Hoffman ..343/833 [73] Assignee: The United States of America as primary Exami"e, Eii Lieberman represented y the Air Force Attorney-Harry A Herbert, Jr. et al. [22] Filed: July 16, 1971 ABSTRACT [21] APPI' 163224 Disc on rod antenna radiating elements having bifilar helix feeds are arranged in a particular concentric cir- US. Cl. 343/785, 343/833, cle type array configuration to achieve gain im- 343/8 3/880, 3 3/895 proved elipticity and size and weight economies. Ele- [51] Int. Cl. ..H0lq 3/26 ment spacing is adjusted to prevent element collecting [58] Field of Search ..343/785, 844, 846, 854, 880, aperture overlap. A collapsible segmented dielectric 343/895, 833 rod in combination with ring members of radial wire segments are utilized to provide an unfurlable array in one preferred embodiment.

8 Claims, 12 Drawing Figures A A HNTENNR ELEMENTS A 2 l l I E E ELEMENT FEID AND- E Z MATCHING NETWORKS l l l L L Low Loss LIGHT wEmH-r L a;

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A-r-roRNEVs PATENTEfllnv 1 i912 llW IlllI lr SHEET 3 BF 3 FIG] FIEJII Heux FEED/ Pom-r 2 I HI FIEJO WILLIAM B KOLL INVENTO ROBERT G. HIGGINS ATTORNEYS SATELLITE UNFURLABLE ANTENNA ARRAY BACKGROUND OF THE INVENTION This invention relates to traveling wave type antenna elements and to electronically steerable arrays of such elements. The invention also comprehends unfurlable antenna arrays of the same type suitable for satellite use.

Antenna arrays for satellite applications must be lightweight, unfurlable and have high gain and good circular polarization. The current state of the art does not provide lightweight unfurlable apparatus that has the electrical characteristics required in large scan area electronically controlled antenna arrays. Reduction in gain due to element collecting aperture overlap has been a problem with some arrays. Most available radiating element require many turns of the feed coupling structure to provide acceptable beam elipticity. This adds to the length and weight of the radiating elements and is a detriment in satellite applications. There is currently a need therefore for new approaches and unique structure that will obviate these and other problems encountered when state of the art antenna structures are utilized for space purposes. The present invention is directed toward accomplishing these and other ends.

SUMMARY OF THE INVENTION The invention comprehends traveling wave type antenna radiating elements having unique bifilar helical signal coupling means; the use of such radiating structures in particular array configurations that achieve optimum elipticity and gain; and unique element structure that provides for lightweight unfurlable design for satellite applications while retaining desired electrical characteristics.

The basic radiating element is a disc on rod device having a ground plane member in close parallel relationship with an end disc. The discs are of conductive material, of equal or unequal size and are unifonnly spaced along the rod. A bifilar helix positioned between the ground plane member and the end disc couples signals to the element. The input feed circuit to the bifilar helix includes a 90 hybrid and matching impedances. For satellite application, the rod is replaced by an expandable truss-type fiberglass structure, the discs are replaced by rings of flexible wire segments and the ground plane member is replaced by a wire grid. The rings of wire segments have varying diameters giving the radiating element tapered effect in order to provide electrical characteristics similar to those of the disc on rod device.

The radiating elements are arranged in a concentric circle type array and electronic scanning of the array is accomplished in any conventional manner. Element spacing in the array is minimized consistent with element collecting aperture overlap elimination. The elements are mounted on structural members representing common radii of the concentric circles. The structural members can be expandable and unfurlable for satellite applications.

It is a principal object of the invention to provide a new and improved traveling wave type antenna radiating element.

is another object of the invention to provide a new and improved electronically scanned array of such radiating elements.

It is another object of the invention to provide an expandable traveling wave type antenna radiating element suitable for satellite use.

It is another object of the invention to provide a lightweight unfurlable antenna array of radiating elements of the type described.

It is another object of the invention to provide an antenna array of the type described having improved elipticity.

These, together with other objects, features and advantages of the invention will become more readily apparent from the following detailed description taken in conjunction with the illustrative embodiment in the accompanying drawings.

DESCRIPTION OF DRAWINGS FIG. 1 is a system block diagram of the electronically scanned antenna array of the present invention;

FIG. 2 illustrates the concentric circle type array configuration comprehended by the invention;

FIG. 3 is a schematic illustration of a single radiating element of FIG. 2;

FIG. 4 is a schematic detail of the ground plane element utilized in the unfurlable embodiment of the invention;

FIG. 5 is a schematic detail of the wire ring type disc member utilized in the unfurlable embodiment of the invention;

FIG. 6a is a structural detail of the disc support member utilized in the unfurlable embodiment of the invention;

FIG. 6b is a plan view of the structure of FIG. 6a;

FIG. 7 illustrates schematically the disc size arrangement utilized in the unfurlable embodiment of the invention;

FIG. 8 illustrates the bifilar helix signal coupling member of FIG. 3;

FIG. 9 is a plan view of the disc on rod embodiment of the invention;

FIG. 10 illustrates aportion of an elevational view of the disc on rod embodiment; and,

FIG. 11 illustrates schematically the elements feed and matching netowrk.

general block diagram of the antenna system comprehended by the invention. This comprises a phase scanned antenna array whose basic components consist of disc on rod antenna elements 12 (solid or unfurlable), element feed and matching networks 13, low loss lightweight transmission lines 14, power divider network 16, diode switched delay lines 15, and diplexer 17.

The Antenna Elements are the high-gain radiating component which converts electromagnetic energy from a guided mode of propagation to free-space propagation. The Element Matching and Feed Network divides and properly phases the electromagnetic energy for the bifilar helix feed (hereinafter described). The Low-Loss Lightweight Transmission Lines serve to transfer the energy from the hub to the array elements. These units also serve as the mechanical support members of the elements. The Power Divider Network is that device which properly divides and phases the electromagnetic energy as required by the arrayed elements. The Diode-Switched Delay Lines perform the function of delaying for beam steering the energy to each element by means of diode switching control. The Diplexer unit provides isolation between the input and output ports to the antenna array by means of frequen cy discrimination.

The antenna elements 12 are arrayed in the concentric circle type configuration illustrated in FIG. 2. Elements 12 are located at the intersections of concentric circles and common radii as shown. Each circle radius r and each radii displacement angle a is a matter of engineering design. It is a principle of the invention however, that element spacing should not be so close as to permit excessive element collecting aperture overlap. The elements can be mounted on radially disposed support members (not shown). In the unfurable embodiment of the invention these support members can be both expandable and unfurlable.

FIG. 3 illustrates, schematically, the essential components of radiating element 12. It comprises a support structure 19, disc members 18, bifilar helix coupling means 20, and ground plane member 21. FIGS. 4, 5, 6a and 6b illustrate the structural details of these components for the unfurlable embodiment of the invention. Ground plane member 21 as illustrated by FIG. 4 comprises a wire grid 22 made up of wire rings 23 and radial wire segments 24. FIG. illustrates a disc member 18 of radial wire segments 25. Wire segments 25 can be flexible beryllium copper wire segments of appropriate length. An expandable support structure 19 is shown in detail by FIGS. 6a and 6b. The longitudinal members 26 are small diameter uniaxial glass fiber rods. Ring members 27 are also made of small diameter uniaxial glass fiber rods. The diagonal supports 28 can be of a plastic cord such as DACRON or the like. The longitudinal members are jointed to provide pivot member 29 at appropriate points along their lengths to permit collapsable storage. This is accomplished by a clockwise or counterclockwise stress being put on the support member 19.

The disc members of the unfurlable embodiment are made of varying diameters similar to those of the solid disc-on-rod elements for improved frequency bandwidth characteristics. This is illustrated schematically by discs 30, 31, 32 of FIG. 7. Larger discs 32 are adjacent to the bifilar helix coupling member and smaller discs 30 are at the end of the element giving it a tapered effect.

The bifilar helix coupling structure 20 is illustrated in detail in FIG. 8. It comprises helix 33 and helix 34, which members are separated by 90 and are positioned in the relationship shown between ground plane member 21 and the first radiating element disc member.

A solid element embodiment of the invention is illustrated by the details of FIGS. 9 and 10. This embodiment comprehends an aluminum tube support structure 36, a solid aluminum ground plane member, aluminum plate discs 35 and solid aluminum tubing helix members.

The element feed and matching network illustrated in FIG. 11 performs two functions. The first is to provide an equal power split and 90 phase difference to feed each of the helical radiating elements in the bifilar configuration, and also to provide impedance transformation from the hybrid to the helix elements.

A normal six-tum helix will provide good circular polarization over a limited frequency band, while a very short helix has generally poor circularity. Good circularity can be obtained by situating two short helices orthogonally in space and feeding one out of phase with the other. The elliptically polarized fields of each are then properly combined to yield good circularity in the far field. A broad-band stripline 90 hybrid 43 is used to properly phase and combine energy from the helices. The hybrid characteristic impedance must be matched to the helix and therefore, a matching section is required to transform the hybrid impedance to the approximate input impedance-of the helical radiating elements.

The element feed and matching network 13 is shown pictorially in FIG. 11. It is fabricated in a stripline configuration. The circuit boards 38 take the shape of an L so that the output terminals 41, 42 will align with the starting points of the helical radiating elements. The outputs of the 90 hybrid 43 (points A and B) are connected to tapered (in width) and meandered strip transmission lines 39, 40 which perform the impedance transformation function.

While the invention has been described in presently preferred embodiments it is understood that the words which have been used are words of description rather than words of limitation and that changes with the purview of the appended claims may be made without departing from the scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An antenna radiating element comprising:

a column of spaced parallel conductive discs,

a ground plane member in proximate parallel relationship to one terminal disc of said column,

a bifilar helix signal coupling means disposed between said ground plane member and said terminal disc, and

a 90 hybrid feed circuit connected to said bifilar helix.

2. An antenna array comprising aplurality of radiating elements arranged in concentric circles, each said radiating element comprising:

a column of spaced parallel conductive discs,

a ground plane member in proximate parallel relationship to one terminal disc of said column,

a bifilar helix signal coupling means disposed between said ground plane member and said terminal disc, and

a 90 hybrid feed circuit connected to said bifilar helix.

3. An antenna array as defined in claim 2 wherein said radiating elements are located at intersections of said concentric circles and selected uniformly spaced common radii thereof.

4. An antenna array as defined in claim 3 wherein radiating element spacing is adapted to substantially eliminate element collecting aperture overlap.

5. An antenna radiating element comprising:

an extendable support structure of dielectric materimeans comprising rings of radial wire segments establishing a plurality of parallel electrically conductive planes along said support structure,

a wire grid ground plane member in proximate parallel relationship to the wire segment ring at one end of said support structure,

lel relationship to the wire segment ring at one end of said support structure,

a bifilar helix signal coupling means disposed between said ground plane member and said wire segment ring, and,

a hybrid feed circuit connected to said bifilar helix.

7. An unfurlable antenna array as defined in claim 6 wherein said radiating elements are located at intersections of said concentric circles and selected uniformly spaced common radii thereof.

8. An unfurlable antenna array as defined in claim 7 wherein radiating element spacing is adapted to substantially' eliminate elements collecting aperture overlap.

* I I i 

1. An antenna radiating element comprising: a column of spaced parallel conductive discs, a ground plane member in proximate parallel relationship to one terminal disc of said column, a bifilar helix signal coupling means disposed between said ground plane member and said terminal disc, and a 90* hybrid feed circuit connected to said bifilar helix.
 2. An antenna array comprising a plurality of radiating elements arranged in concentric circles, each said radiating element comprising: a column of spaced parallel conductive discs, a ground plane member in proximate parallel relationship to one terminal disc of said column, a bifilar helix signal coupling means disposed between said ground plane member and said terminal disc, and a 90* hybrid feed circuit connected to said bifilar helix.
 3. An antenna array as defined in claim 2 wherein said radiating elements are located at intersections of said concentric circles and selected uniformly spaced common radii thereof.
 4. An antenna array as defined in claim 3 wherein radiating element spacing is adapted to substantially eliminate element collecting aperture overlap.
 5. An antenna radiating element comprising: an extendable support structure of dielectric material, means comprising rings of radial wire segments establishing a plurality of parallel electrically conductive planes along said support structure, a wire grid ground plane member in proximate parallel relationship to the wire segment ring at one end of said support structure, a bifilar helix signal coupling means disposed between said ground plane member and said wire segment ring, and, a 90* hybrid feed circuit connected to said bifilar helix.
 6. An unfurlable antenna array comprising a plurality of radiating elements arranged in concentric circles, each said radiating element comprising: an extendable support structure of dielectric material, means comprising rings of radial wire segments establishing a plurality of parallel electrically conductive planes along said support structure, a wire grid ground plane member in proximate parallel relationship to the wire segment ring at one end of said support structure, a bifilar helix signal coupling means disposed between said ground plane member and said wire segment ring, and, a 90* hybrid feed circuit connected to said bifilar helix.
 7. An unfurlable antenna array as defined in claim 6 wherein said radiating elements are located at intersections of said concentric circles and selected uniformly spaced common radii thereof.
 8. An unfurlable antenna array as defined in claim 7 wherein radiating element spacing is adapted to substantially eliminate elements collecting aperture overlap. 